Switched capacitor transducer

A capacitive transducer comprising:

• first and second variable capacitors comprising first and second fixed capacitor electrodes and a common capacitor electrode interposed between the first and second electrodes, the common electrode being displaceable from a rest position to vary the capacitances of the capacitors as a function of a parameter being measured;
• a voltage source providing a common voltage, a main reference voltage and an intermediate voltage;
• a charge integrator coupled to the common capacitor electrode and responsive to changes in the capacitances for generating an output voltage;
• means for biasing the charge integrator input to a biasing voltage;
• an attenuating amplifier having an inverting input coupled to the output of the charge integrator and a non-inverting input coupled to the intermediate reference voltage for generating a bridge signal which varies as a function of changes in the capacitances;
• first and second switches for connecting the first and second electrodes to the main reference voltage and the common voltage, respectively;
• a third switch for connecting the common electrode to the charge integrator input;
• means for opening and closing the said first second and third switches synchronously;
• fourth switches for connecting the first and second electrodes to the bridge signal and the common electrode to the biasing voltage;
• means for closing the fourth switches only when the first, second and third switches are open;
• whereby the common electrode is held at the biasing voltage, and charge changes on the common electrode are applied to the charge integrator to produce the output voltage in accordance with the relative capacitances of the first and second capacitors.

A capacitive transducer comprising:

• first and second variable capacitors having capacitances C.sub.r and C.sub.p, respectively, comprising first and second fixed capacitor electrodes and a common capacitor electrode interposed between the first and second electrodes, the common electrode being displaceable from a rest position to vary the capacitances of the capacitors as a function of a parameter being measured;
• a voltage source providing a ground voltage, a main reference voltage V and an intermediate voltage V.sub.i ;
• a charge integrator coupled to the common capacitor electrode and responsive to changes in the capacitances for generating an output voltage V.sub.o ;
• means for biasing the charge integrator input to a biasing voltage;
• an attenuating amplifier having an inverting input coupled to the output of the charge integrator through an input resistance R.sub.i and having a feedback resistance R.sub.f, and a non-inverting input coupled to the intermediate reference voltage V.sub.i for generating a bridge signal V.sub.b =V/2(1-(C.sub.p -C.sub.r)/(C.sub.p +C.sub.r));
• first and second switches for connecting the first and second electrodes to the main reference voltage and the common voltage, respectively;
• a third switch for connecting the common electrode to the charge integrator input;
• means for opening and closing the said switches synchronously;
• fourth switches for connecting the first and second electrodes to the bridge signal and the common electrode to the biasing voltage;
• and
• means for closing and reopening the fourth switches only when the first, second and third switches are open;
• whereby the charge integrator produces the output voltage V.sub.o =(R.sub.i /R.sub.f) (V.sub.i (R.sub.f /R.sub.i +1)-V.sub.b).

A capacitive transducer circuit comprising:

• first and second fixed capacitor plates and a third movable capacitor plate, means for mechanically suspending the third plate between the first and second plates for complemental movement relative thereto;
• output circuit means having an input and an output;
• first switch means having periodic operating times for connecting the first and second plates across a substantially non-varying unidirectional voltage source and, simultaneously therewith, connecting the third capacitor plate to the input of the output circuit means;
• second switch means having periodic operating times for connecting the first and second plates to a common potential and, simultaneously therewith, disconnecting the third plate from said output circuit input;
• and
• means for rapidly and complementally operating the first and second switch means such that the periodic operative times thereof are non-overlapping wherein the output circuit means comprises a signal integrator, and wherein the signal integrator has inverting and non-inverting inputs, said first switch means being operative to connect the third plate to the non-inverting input and said second switch means being operative for connecting the third plate to the inverting input.